A gas internal combustion type nailing machine is conventionally known (for example, see the patent reference 1) and, in this type of nailing machine, there is also known a nailing machine which aims at increasing the output energy thereof by supercharging compressed air into a combustion chamber.
In these well-known gas internal combustion type nailing machines, there are taken measures to maintain a proper air-fuel ratio in order to secure a good combustion state and, for this purpose, there is provided means for adjusting a fuel injection amount based on an air supply amount into the combustion chamber.
For example, a certain known gas internal combustion type nailing machine of a supercharge type has a structure which supplies compressed air and fuel into a combustion chamber through their individual supply pipes. A supply of a predetermined amount of fuel to be supplied into the combustion chamber is carried out using a quantity measuring valve to be controlled by mechanical or electronic control means provided in the fuel supply pipe (for example, see the patent reference 2).    [Patent Reference 1] JP-B-04-048589    [Patent Reference 2] US 2004/0134961A1
In the above gas internal combustion type nailing machine, in order to maintain a proper air-fuel ratio, the fuel supply amount is adjusted based on the air supply amount. This adjustment of the fuel supply amount is carried out by linking the air supply amount and the fuel supply amount with each other. In the fuel supply using the quantity measuring valve to be controlled by the mechanical or electronic control means of the gas internal combustion type nailing machine disclosed in the above patent reference 2 as well, the fuel supply amount is adjusted in linking with the air supply amount.
Here, according to the above method for supplying the fuel in linking with the air supply amount, for example, even when, in the gas internal combustion type nailing machine of a supercharge type, an excessive amount of compressed air is supplied for some reason and thus the supercharge pressure exceeds a given pressure value, as long as the compressed air is supplied continuously, the fuel is supplied based on the air supply amount.
However, by a combustion in a high supercharge pressure exceeding a given pressure value, the explosion energy of such combustion exceeds the output energy that is set previously. And, when such excessive output energy is generated, the nailing machine is excessively loaded physically, which has ill influences on the durability and safety of the nailing machine. Therefore, from the viewpoint of securing the durability and safety of the nailing machine, it is necessary to take effective measures to eliminate such ill influences.